The present invention relates to a Co—Cr—Pt—B alloy sputtering target having a uniform and fine rolled structure with minimal segregation and residual stress upon casting.
In recent years, a Co—Cr—Pt—B alloy is being used as a sputtering target for forming the magnetic film of a hard disk.
To form a film by sputtering method, a substrate which is formed of a positive electrode and a target which is formed of a negative electrode are faced each other, a high voltage is applied between such substrate and target under an inert gas atmosphere, and an electric field are generated.
The sputtering method employs the principle in which plasma is formed under the above-mentioned high impressed voltage, the positive ions within this plasma collide with the target (negative electrode) surface, whereby the atoms structuring the target is expelled, and the film is formed by the expelled atoms adhering to the opposing substrate surface.
As the sputtering method, employed may be a high frequency sputtering (RF) method, magnetron sputtering method, DC (direct current) sputtering method and so on, these methods are suitably adopted in accordance with the target material or deposition conditions.
Generally, upon manufacturing a sputtering target, such target is demanded of having a uniform and fine structure, and without any defects such as pores therein. When the target structure is uneven and numerous defects exist, these defects are reflected in the deposited film, and an uneven film inferior in performance will be formed. Further, this will also raise the problem of the increased generation of particles upon forming a sputtered film.
Moreover, there is another problem in that the coercive force value and variations thereof of the thin film medium formed via sputtering will change due to the used target.
Thus, attempts have been made for obtaining a uniform and fine processed structure by performing rolling processing after melting and casting the target material (c.f. Patent Document 1 for example).
Nevertheless, with a Co—Cr—Pt—B alloy casting, there is a problem in that segregation and residual stress resulting from the unevenness of the cooling speed during solidification would occur. Segregation and residual stress causes unevenness and defects in the sputtered deposition, and it is necessary to eliminate these as much as possible.
Although it is possible to suppress such segregation and residual stress by strictly controlling the casting conditions, the once generated segregation and residual stress must be removed thereafter.
[Patent Document 1]
Gazette of Japanese Patent Laid-Open Publication No. 2002-69625